I. Field of the Invention
The present invention relates to fluid systems for controlling the movement of a fluid cylinder and, in particular, the present invention relates to a closed-loop, hydrostatic system in which the output of a pump is selectively directed to a fluid cylinder to expand and retract the same while a separate pressure chamber associated with the cylinder is communicated to an accumulator that functions to generate a force that counterbalances the load carried by the cylinder throughout the expansion and retraction stages of the cylinder.
II. Description of the Prior Art
Heretofore numerous fluid systems have been employed for controlling the rate of movement of hydraulic motors and, in particular, systems which have single-rod pistons that have pressure responsive surfaces of equal areas. Thus, the force available for extension and retraction is substantially the same. An example of such a cylinder and a system for operating the cylinder is disclosed in my U.S. Pat. No. 3,744,375 issued July 10, 1973. An application in which such a system might be employed is a lift system as in the raising and lowering of substantial automation equipment. It has been known in the past to provide a separate hydraulic and/or mechanical counterbalance for the press so that the cylinders that are raising and lowering the equipment provide only the force of lift whereas the weight of the equipment is carried by some type of counterbalance system. Systems that may be employed to counterbalance a load are disclosed in U.S. Pat. Nos. 3,942,323, 3,946,559 and 4,202,174. Each of these systems differs from the present invention in that they employ a separate system for the counterbalance function as opposed to the unique and unitary system disclosed in this present application.
It would therefore be desirable to provide a fluid system that has a multi-pressure chamber fluid cylinder wherein one of the pressure chambers is in communication selectively with an accumulator to provide a counterbalance of the load that the cylinder is displacing.
III. Prior Art Statement
In the opinion of applicant and applicant's attorneys the aforementioned prior art represents the most relevant prior art of which applicant and applicant's attorneys are aware.